Address review comments

Author: noti0na1

compiler/src/dotty/tools/dotc/cc/Capability.scala

@@ -603,6 +603,10 @@ object Capabilities:
     def assumedContainsOf(x: TypeRef)(using Context): SimpleIdentitySet[Capability] =
       CaptureSet.assumedContains.getOrElse(x, SimpleIdentitySet.empty)
 
+    /** The type representing this capability.
+     *  Note this method does not distinguish different `RootCapability` instances,
+     *  and should only be used for printing or phases not related to CC.
+     */
     def toType(using Context): Type = this match
       case c: RootCapability => defn.captureRoot.termRef
       case c: CoreCapability => c

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -203,7 +203,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         )
       isUniversal
       || !refs.elems.isEmpty && refs.elems.forall(_.isCapOrFresh) && !ccVerbose
-    case (ref: TermRef) :: Nil => ref.symbol == defn.captureRoot
+    case ref :: Nil => ref.isCapRef
     case _ => false
 
   protected def toTextGeneralCaptureSet(refs: GeneralCaptureSet): Text = refs match
@@ -312,7 +312,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         def arrowText: Text = restp match
           case AnnotatedType(parent, ann) if ann.symbol == defn.RetainsByNameAnnot =>
             ann.tree.retainedSet.retainedElementsRaw match
-              case (ref: TermRef) :: Nil if ref.symbol == defn.captureRoot => Str("=>")
+              case ref :: Nil if ref.isCapRef => Str("=>")
               case refs => Str("->") ~ toTextRetainedElems(refs)
           case _ =>
             if Feature.pureFunsEnabled then "->" else "=>"

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -435,7 +435,7 @@ object RefChecks {
 
       def emitOverrideError(fullmsg: Message) =
         if !(hasErrors && member.is(Synthetic) && member.is(Module) || member.isDummyCaptureParam) then
-          // suppress errors relating to synthetic companion objects if other override
+          // suppress errors relating to synthetic companion objects and capture parameters if other override
           // errors (e.g. relating to the companion class) have already been reported.
           if (member.owner == clazz) report.error(fullmsg, member.srcPos)
           else mixinOverrideErrors += new MixinOverrideError(member, fullmsg)